The long-term objective of this project is a better understanding of the role of genetics in human behavior disorders. Stuttering is being studied as a model trait because it is intrinsically interesting, it is a common disorder of children, and it is relatively easy to diagnose. Preliminary analyses using genetic models suggest a large genetic component, possibly even a single major locus, responsible for the disorder. As part of an ongoing study, data on nearly 600 families of stutterers have been collected and data on children not yet through the age of risk have been updated as much as five years after the initial interview. We now propose an intensive study of selected large families incorporating genetic linkage, and measures of speech-related auditory processing. These new and much more extensive data are being gathered to provide the necessary information to increase ability to isolate and characterize any genetic component, to identify possible etiological heterogeneities, and to confirm or reject hypotheses of cultural transmission. Concomitantly with the collection and analyses of data on stuttering we will pursue development of new genetic models appropriate for disorders like stuttering.